Micro spray nozzle plates with orifices of a few micrometers or smaller, created by means of semiconductor manufacturing techniques, need to be packaged for connection to e.g. a spray pump or syringe according to pharmaceutical manufacturing protocols. Liquids, to be sprayed through spray nozzles with small orifices, often require the use of one, or a series of prefilter plates to prevent clogging of the spray orifices. It is known to make prefilter plates also by means of semiconductor manufacturing or micromachining. For medicinal or pharmaceutical purposes the use of glue, solvents or sealing agents, to mount a spray nozzle plate and/or a prefilter in a spray nozzle unit, is not preferable. Plastic materials to be used in spray nozzle units are typically medical grade plastics, which have an acceptable low extractables and leachables profile. Most medical grade plastics are thermoplastic materials, such as polyethylene (PE), polypropylene (PP), polyvinylchloride (PVC), polyetheretherketone (PEEK), cyclic olefin polymer (COP), poly sulfone (PS), polyoxymethylene (POM), polycarbonate (PC), or polyamid (PA) and may be applied as part of the primary package of a medicinal fluid. The spray nozzle unit therefore comprises a medical grade thermoplastic package holding the nozzle plate with one or more prefilter plates, and it further needs to be packaged according to pharmaceutical manufacturing protocols in a bioburden controlled Good Manufacturing Practice (GMP) environment. The spray nozzle unit would ideally be used in an aerosol or spray device where no preservative is added to the medicinal liquid. In that case a spray nozzle unit needs to function as an impenetrable barrier for microbes to prevent them from entering the container of the spray device via the nozzle plate side.
In operation the spray nozzle unit is subjected to high operating liquid pressures at varying temperatures and there is a risk of internal leakage and loss of bacterial integrity between the polymer parts of the package and the nozzle plate or the prefilter. Moreover, being able to handle high operating pressures it is important to ensure that the spray nozzle plate cannot come loose or even ejected, thereby potentially hitting a person using the device. Typical operating pressures for aerosol and spray devices lie between 1 and 50 Bar, with possibly higher peak pressures at start and end of the spraying mode.